The present invention relates to sem conductor substrates, and more particularly to a semiconductor substrate fabricated to include hermetically-sealed electronic circuitry as well as non-hermetically-sealed electrodes thereon so as to form an implantable sensor or other implantable electronic device.
In U.S. Pat. No. 5,660,163, there is disclosed an implantable glucose sensor which is fabricated on a ceramic substrate. Working electrodes and other elements associated with the sensor are exposed to a conductive fluid contained within a reservoir or inner sheath that covers the substrate. An outer sheath is also placed over the sensor, with a window formed over one of the working electrodes. A selected enzyme, such as glucose oxidate (GO), is placed within the window. As disclosed in the '163 patent, five wires or conductors are attached to the electrodes and connected to electronic circuitry, e.g., a circuit such as is shown in FIG. 3 of U.S. Pat. No. 5,660,163. U.S. Pat. No. 5,660,163 is incorporated herein by reference.
Additional features, aspects and improvements of a glucose sensor of the type disclosed in U.S. Pat. No. 5,660,163 (hereafter the “'163 patent”) are further disclosed in U.S. patent application Ser. No. 08/953,817, filed Oct. 20, 1997; Ser. No. 08/954,166, filed Oct. 20, 1997; and Ser. No. 08/928,867, filed Sep. 12, 1997; all of which are assigned to the same assignee as the present application, and each of which above-referenced patent applications is incorporated hereon by reference.
As disclosed in the referenced patent applications, an improved implantable sensor may be fabricated by placing the electrodes on one side of the substrate, and by also placing an integrated circuit (IC) chip on the other side of the substrate, along with other needed electronic components, e.g., a capacitor(s), thereby forming a hybrid electronic circuit on the side of the substrate opposite the electrodes that is used to control or drive the sensor (i.e., sense the electrical current flowing to the electrodes, from which current the amount of oxygen near the electrodes can be determined, from which determination, the amount of glucose to which the sensor is exposed can also be determined), as well as to send and receive information, data, and/or power from an external location over a two-conductor transmission line. The IC chip and other electronic components are hermetically sealed under a metal cover, the edges of which are hermetically bonded to the substrate. Electrical connection is established with the IC chip and other sealed components through stair-step vias or passageways that traverse through the substrate. Several of these types of sensors may be daisy-chained together, using just two conductors, as required. The outer sheath encircles the entire substrate, both the electronic circuit side with its metal cover, and the sensor electrode side, with its electrodes, saline solution reservoir and enzyme-filled window.
Disadvantageously, the sensor described in the referenced patent and patent applications is relatively thick. For many implantable applications, a thinner sensor is needed. Hence, there remains a need for yet a smaller sensor that performs all of the same functions as the prior sensor, i.e., that provides working electrodes exposed to a saline solution, with a selected enzyme placed over one electrode, and with hermetically-sealed electronic circuitry controlling the sensor and communicating with other sensors and an external control unit The present invention advantageously addresses these and other needs.